1. Field of the Invention
The present invention relates to a liquid crystal display (hereinafter referred to as xe2x80x9cLCDxe2x80x9d) device, and more particularly to a backlight assembly and an LCD device having the same for improving a wiring connection of electrode lines of lamps that provide the light source for the backlight of the LCD device to minimize the size of the LCD device and to reduce the manufacturing cost.
2. Description of the Related Art
In recent years, information processing appliances have been rapidly developed to have a variety of forms and functions and faster information processing speed. The information processed in such an information processing apparatus has an electrical signal format. A display device serving as an interface is required for a user to confirm the information processed in the information processing apparatus by the naked eyes.
Currently, an LCD device having functions of manifesting full-color and attaining high resolution while attaining lightweight and small size compared with the conventional CRT-type display device. As the result, the LCD device has been widely available as a computer monitor that is a representative information processing apparatus, a household wall-hanging television and so on.
The LCD device applies electric fields to a liquid crystal layer to convert its molecular arrangement. Then, the LCD device converts the changes of the optical properties such as birefringence, optical linearity, dichroism and optical scattering characteristic of liquid crystal cells according to the molecular arrangement, and uses the modulation of the light by the liquid crystal cells.
The LCD device is largely sorted into a TN (Twisted Nematic) type and a STN (Super-Twisted Nematic) type. The liquid crystal display device is, according to the driving method, sorted into an active matrix display type, which uses a switching device and a TN liquid crystal, and a passive matrix type, which uses an STN liquid crystal.
A distinguishable difference of two types is that the active matrix display type is applied to a TFT-LCD that drives the LCD by using a TFT and the passive matrix display type does not use a complicated circuit associated with a transistor.
Also, according to a method of using a light source, it is classified into a transmissive LCD device using a backlight and a reflective LCD using an external light source.
Despite the increased weight and volume, the transmissive LCD device using the backlight as the light source is widely used, because it can independently display images without using an external light source.
FIG. 1 is an exploded perspective view schematically showing a conventional LCD device. FIGS. 2, 3 and 4 are circuit diagrams more specifically showing lamps of the backlight assembly shown in FIG. 1 and configurations of an inverter module for driving the lamps.
Referring to FIG. 1, an LCD device 900 is formed by an LCD module 700 for displaying an image by being supplied with an image signal, and a face panel case 810 and a rear panel case 820 for retaining LCD module 700. Here, LCD module 700 has a display unit 710 including an LCD panel 712 for displaying the image.
Display unit 710 includes LCD panel 712, a data-side printed circuit board (PCB) 714, a gate-side PCB 719, a data-side tape carrier package 716 and a gate-side tape carrier package 718.
LCD panel 712 has a thin film transistor (TFT) substrate 712a, a color filter substrate 712b and a liquid crystal (not shown).
TFT substrate 712a is a transparent glass substrate formed with thin film transistors on a matrix. Source terminals of the TFTs are connected with data lines, and gate terminals are connected with gate lines. Also, drain terminals are formed with pixel electrodes consisting of a transparent conductive material such as Indium-Tin-Oxide (ITO).
Once electrical signals are supplied to the data lines and gate lines, the source terminals and gate terminals of respective TFTs receive the electrical signals. In accordance with the input of the electrical signals, the TFTs are turned-on or turned-off to supply the electrical signals required for forming the pixels to the drain terminals.
A color filter substrate 712b is provided facing TFT substrate 712a. Color filter substrate 712b is formed via a thin film processing of RGB pixels that display predetermined colors when light goes through. Color filter substrate 712b is coated with a common electrode formed of ITO over the front surface thereof.
When the power is supplied to the gate terminals and source terminals of the transistors on the aforementioned TFT substrate 712a, an electric field is formed between the pixel electrode and common electrode of color filter substrate 712b. This electric field changes the alignment angle of the liquid crystal injected between TFT substrate 712a and color filter substrate 714b. The light transmissivity changes in accordance with the alignment angle. This allows to have a desired pixel status.
In order to control the alignment angle of the liquid crystal of LCD panel 712 and the period of aligning the liquid crystal, a driving signal and a timing signal are supplied to the gate line and data line of the TFT. As shown in the drawing, tape carrier package 716 that is one of a soft circuit board that determines the period of applying the data driving signal is attached to the source side of LCD panel 712. Also, gate-side tape carrier package 718 that is one of the soft circuit board that determines the period of applying the gate driving signal is attached to the gate side thereof.
Data-side PCB 714 and a gate-side PCB 719 for respectively supplying the driving signals to the gate line and data line after being externally received with an image signal out of LCD panel 712 are respectively connected to data tape carrier package 716 on the data line side of LCD panel 712 and gate tape carrier package 718 on the gate line side thereof. Data-side PCD 714 is formed of a source portion that receives the image signal generated from an external information processing apparatus (not shown) such as a computer to supply a data driving signal to LCD panel 712. Also, gate-side PCB 719 is formed with a gate portion for supplying a gate driving signal to the gate line of LCD panel 712. In other words, data-side PCB 714 and gate-side PCB 719 generate the gate driving signal and data signal for driving the LCD device and a plurality of timing signals for supplying the driving signals at the appropriate period, so that the gate driving signal is supplied to the gate line of LCD panel 712 via gate-side tape carrier package 718 and the data signal is supplied to the data line of LCD panel 712 via data tape carrier package 716.
A backlight assembly 720 for supplying the consistent light to display unit 710 is provided under the display unit 710. Backlight assembly 720 includes 1st and 2nd lamp units 723 and 725 equipped at both ends of LCD module 700 for generating the light. 1 st and 2 nd lamp units 723 and 725 are respectively formed by 1st and 2nd lamps 723a and 723b and 3 rd and 4 th lamps 725a and 725b, which are respectively shielded by first and second lamp covers 722a and 722b. 
Light guide plate 724 is large enough to correspond to LCD panel 712 of display unit 710 to underlie LCD panel 712 for changing the path of light while guiding the light generated from 1st and 2nd lamp units 723 and 725 toward display unit 710. In FIG. 1, light guide plate 724 is of an edge-type having a uniform thickness, which has lamp units at both ends of light guide plate 724 for enhancing the light efficiency. The number of first and second lamp units 723 and 725 may be properly set to be arranged by considering the overall balance of LCD device 900.
A plurality of optical sheets 726 are provided to the upper side of light guide plate 724 to make the luminance of light outgoing from light guide plate 724 toward LCD panel 712 consistent. A reflecting plate 728 is installed at the lower side of light guide plate 724 to reflect the light leaking from light guide plate 724 toward light guide plate 724 so as to enhance the light efficiency.
Display unit 710 and backlight assembly 720 are fixedly supported by a mold frame 730 which is a receiving container. Mold frame 730 is shaped as a rectangular box with the upper plane opened. Additionally, a chassis 740 is provided for externally bending data-side PCB 714 and gate-side PCB 719 of display unit 710 to fix them to the lower plane of mold frame 730 while preventing the deviation of display unit 710. Chassis 740 is opened for exposing LCD panel 710, of which sidewall portion is inwardly bent in the perpendicular direction to cover the upper periphery of LCD panel 710.
Meantime, even not shown in FIG. 1, LCD device 900 is equipped with a 1st inverter INV1 as shown in FIG. 2 for driving 1st, 2nd, 3rd and 4th lamps 723a, 723b, 723c and 723d. 
Referring to FIG. 2, 1st inverter INV1 has 1st and 2nd transformers T1 and T2, and 1st and 2nd stabilizing circuits 723e and 725e. An output terminal at the high voltage level of a secondary side of 1st transformer T1 is connected to respective input sides of 1st and 2nd lamps 723a and 723b, i.e., the first electrode. 1st and 2nd ballast capacitors C1 and C2 are interposed between the output terminal at the high voltage level of the secondary side of 1st transformer T1 and the first electrodes of 1st and 2nd lamps 723a and 723b. In association with output sides of 1st and 2nd lamps 723a and 723b, i.e., second electrodes, 1st and 2nd return wires (hereinafter referred to as xe2x80x9cRTNxe2x80x9d) 723c and 723d respectively extend long to 1st stabilizing circuit 723e within 1st inverter INV1. 1st and 2nd RTNs 723c and 723d are connected to 1st stabilizing circuit 723e to supply a feedback current. Referring to FIG. 2, first electrodes of 3rd and 4th lamps 725a and 725b are connected to output terminals at the high voltage level of a secondary side of 2nd transformer T2 by interposing 3rd and 4th ballast capacitors C3 and C4. Second electrodes of 3rd and 4th lamps 725a and 725b are connected to 2nd stabilizing circuit 725e within 1st inverter INV1 via 3rd and 4th RTNs 725c and 725d which extend toward 1st inverter INV1, thereby supplying the feedback current.
However, when a single transformer is utilized to drive the plurality of lamps and the electrodes of the lamps are connected in parallel with each other as described above, the current supplied from single transformer is separately supplied to respective lamps. Accordingly, the current applied to respective lamps has a current difference as indicated by the Table 1 below due to a variable load property of the lamp and a difference of a leakage current. Such a current difference becomes large as the lamp current supplied from the transformer becomes lower. Consequently, if the total current of the lamp is low, one side of the lamp is not driven to differ the durability of respective lamps.
In order to solve this problem, as shown in FIG. 3, a driving system for corresponding the lamp and transformer one by one has been suggested.
Referring to FIG. 3, a 2nd inverter INV2 has 1st, 2nd, 3rd and 4th transformers T1, T2, T3 and T4 and 1st and 2nd stabilizing circuits 723e and 725e. 1st, 2nd, 3rd and 4th transformers T1, T2, T3 and T4 are respectively driven by 1st, 2nd, 3rd and 4th controllers CT1, CT2, CT3 and CT4. The first electrodes of 1st and 2nd lamps 723a and 723b are connected to the output terminals at the high voltage level of the secondary sides of 1st and 2nd transformers T1 and T2 by interposing 1st and 2nd ballast capacitors C1 and C2. Also, the second electrodes of respective 1st and 2nd lamps 723a and 723b are serially connected to 1st stabilizing circuit 723e within 2nd inverter INV2 by means of respective 1st and 2nd RTNs 723c and 723d. In the same way, the first electrodes of 3rd and 4th lamps 725a and 725b are respectively connected to the output terminals at the high voltage level of the secondary sides of 3rd and 4th transformers T3 and T4 by interposing 3rd and 4th ballast capacitors C3 and C4. In addition, the second electrodes of 3rd and 4th lamps 725a and 725b are serially connected to 2nd stabilizing circuit 725e within 2nd inverter INV2 by means of 3rd and 4th RTNs 725c and 725d, respectively. However, if the lamps are driven by one-to-one corresponding transformers as shown in FIG. 3, the frequency among respective transformers of the inverter is not easily synchronized. Therefore, the lamp generates light flickering, making it impossible to obtain a suitable light source as backlight of the LCD device.
In order to solve the above problem, as shown in FIG. 4, a method has been proposed in which the lamp corresponds to the transformer one by one and the transformers are coupled in pairs.
More specifically, referring to FIG. 4, a 3rd inverter INV3 is formed by 1st, 2nd, 3rd and 4th transformers T1, T2, T3 and T4 and 1st and 2nd stabilizing circuits 723e and 725e. Low voltage level terminals of the secondary sides of 1st and 2nd transformers T1 and T2 are directly connected to low voltage level terminals of the secondary sides of 3rd and 4th transformers T3 and T4. 1st and 2nd transformers T1 and T2 are driven by 1st controller CT1, and 3rd and 4th transformers T3 and T4 are driven by 2nd controller CT2.
On the other hand, the first electrode of 1st lamp 723a is connected to the output terminal at the high voltage level of 1st transformer T1 by interposing 1st ballast capacitor C1, and the first electrode of 2nd lamp 723b is connected to the output terminal at the high voltage level of 2nd transformer T2 by interposing 2nd ballast capacitor C2. The second electrodes of 1st and 2nd lamps 723a and 723b are serially connected to 1st stabilizing circuit 723e within 3rd inverter INV3 by means of 1st and 2nd RTNs 723c and 723d, respectively. Similarly, the first electrode of 3rd lamp 725a is connected to the output terminal at the high voltage level of 3rd transformer T3 by interposing 3rd ballast capacitor C3. Also, the first electrode of 4th lamp 725b is connected to the output terminal at the high voltage level of 4th transformer T4 by interposing 4th ballast capacitor C4. The second electrodes of 3rd and 4th lamps 725a and 725b are serially connected to 2nd stabilizing circuit 725e within 3rd inverter INV3 by means of 3rd and 4th RTNs 725c and 725d, respectively However, although the above-described difficulty of synchronizing the frequency and problem of the flickering phenomenon are solved by coupling the transformers in pairs, the second electrodes of respective lamps are still connected to the stabilizing circuit on the electrical basis by means of the RTN that extends long toward the inverter side. Hence, any increase in the number of lamps not only produces a difficulty in the electrical wiring but also involves a problem of higher manufacturing costs of the backlight assembly.
FIGS. 5A and 5B show the configuration of the lamps and inverter module of the direct-type LCD device.
As shown in FIG. 5A, the LCD device is formed in a manner that lamp 727 that provides the light is arranged on the bottom plane of a mold frame 730 with a reflecting plate 728 interposed therebetween. Because lamp 727 supplies the light source at the rear side of a display unit 710, no light guide plate 724 for guiding the side light source toward display unit 710 side is employed, unlike the edge-type LCD device as shown in FIG. 1.
By reflecting the structural feature, direct-type LCD device 900, as shown in FIG. 5B, is capable of employing a plurality of lamps 727a, 727b, 727c, 727d, 727e, 727f, 727g and 727h. A 4th inverter INV4 shown in FIG. 5B adopts the configuration of 2nd or 3rd inverter INV2 or INV3 shown in FIG. 3 or FIG. 4, in which the connection with the first electrodes of plurality of lamps 727a, 727b, 727c, 727d, 727e, 727f, 727g and 727h is identical to that of 2nd or 3rd inverter INV2 or INV3. Similarly, the second electrodes of plurality of lamps 727a, 727b, 727c, 727d, 727e, 727f, 727gand 727h are connected to a stabilizing circuit (not shown) within 4th inverter INV4 by means of respective RTNs RTN1, RTN2, RTN3, RTN4, RTN5, RTN6, RTN7 and RTN8.
Also in the direct-type LCD device shown in FIG. 5, the second electrodes of the plurality of lamps are connected to the stabilizing circuit of the inverter via separately-provided RTNs as the driving system shown in FIG. 3 or FIG. 4. Consequently, the lamp unit becomes bulky as the number of RTNs increases. Further, the manufacturing cost of the backlight assembly increases as the number of RTNs increases.
In order to solve the above-mentioned problems of the prior art, an object of the present invention is to provide a backlight assembly capable of improving a connection of electrode lines of lamps that supply a light source for backlight of the LCD device to minimize the size of an LCD device and reduce the manufacturing cost.
Another object of the present invention is to provide an LCD device having a backlight assembly capable of improving a connection of electrode lines of lamps that supply a light source for backlight of the LCD device to minimize the LCD device size and reduce the manufacturing cost thereof.
To achieve the above object of the present invention, there is provided a backlight assembly including a light emitting unit formed of a plurality of lamps for generating light, and a light controlling unit for enhancing luminance of the light supplied from the light emitting unit. Here, each of the plurality of lamps respectively have two electrodes that include a first electrode directly connected to an electrode of at least one adjacent lamp and selectively have a second electrode supplied with externally provided driving signals.
A liquid crystal display device for achieving the above object of the present invention includes a backlight assembly having light emitting unit formed of a plurality of lamps for generating light, and light controlling unit for enhancing luminance of the light supplied from the light emitting unit. In addition, a display unit placed on an upper plane of the light controlling unit receives the light from the light emitting unit via the light controlling unit to display an image. Here, each of the plurality of lamps respectively have two electrodes, and the two electrodes include a first electrode directly connected to an electrode of at least one adjacent lamp and selectively have a second electrode supplied with externally-provided driving signals.
At this time, the driving signals are of first and second driving signals having a phase difference of 180xc2x0 from each other, or N (where N is a constant larger than or the same as 2)xe2x80x94numbered driving signals respectively having a phase difference as many as a value obtained by dividing 360xc2x0 by the number of the plurality of lamps. At this time, when the driving signals is N-numbered, the sum of respective phases of the N-numbered driving signals is zero.
Preferably, the light emitting unit has at least two lamps, the at least two lamps are serially connected to each other, and electrodes of the most preceding lamp and the finally succeeding lamp are supplied with the first and second driving signals, respectively.
More preferably, the backlight assembly further has a driving unit for converting the external power source of a DC component into an AC component, and generating the first and second driving signals having the phase different from each other. Also, the driving unit further has a stabilizing circuit for stabilizing current of the plurality of lamps. Thus, low voltage sides of respective secondary sides of the plurality of transformers are connected to the stabilizing circuit, so that the feedback current for stabilizing the current of the plurality of lamps is supplied to stabilizing circuit.
At this time, the light emitting unit is placed to contact one end or both ends of the light controlling unit. When the light emitting unit is placed to one end of the light controlling unit, the light controlling unit is a wedge-type light guide plate that becomes thinner as advancing from one end placed with the light emitting unit to the other opposing end.
Moreover, the light emitting unit may be placed to the lower plane of the light controlling unit. In this case, the light controlling unit is formed by a plurality of optical sheets for making the luminance of the light supplied from the light emitting unit to the display unit consistent.
According to the above-described backlight assembly and liquid crystal display device, the first electrodes of the lamps are respectively connected to the output terminals at the high voltage level of the secondary sides of the corresponding transformers among the transformers constituting the driving unit. Also, the second electrodes of the lamps are directly connected to one another on the electrical basis. The output terminals at the low voltage level of the secondary sides of the transformers are directly connected to the stabilizing circuit to supply the feedback current for stabilizing the current of the lamps to the stabilizing circuit.
Therefore, because the second electrodes of respective lamps are not required to extend to the stabilizing circuit of the inverter module so as to supply the feedback current to the stabilizing circuit, no RTN is utilized. For this reason, the wiring structure of the electrode lines of the lamps employed to the backlight assembly is simplified to to reduce the size of the backlight assembly while reducing the manufacturing cost of the backlight assembly and LCD device.